The present invention relates to a process of and apparatus for washing a semiconductor wafer, various optical or electric parts, jigs for manufacturing those, etc. with vapor and, more particularly, to a vapor washing process and apparatus in which the vapor used for the washing can be made highly pure so that the washing effect is excellent.
In recent years, the degree of integration of semiconductors is markedly increasing, whereby higher cleanliness is required of the surface of semiconductor a wafer. Wafer washing-drying technique is described in detail in "Ultra-pure Water-High Purity Chemical Substance Supply System Proceeding" of the second symposium on Ultra LSI Ultra-Clean Technology, pages 399-419, which symposium was held at Tokyo Hatsumei-Kaikan hall under the auspices of a society for the study of basic semiconductor technology.
As is apparent from the above-mentioned papers, generally, semiconductor wafers are washed with a solvent (triclene, acetone H.sub.2 O.sub.2 -NH.sub.4 OH mixture, etc.) to remove fatty substances adhering to a substrate surface, and with acid-alkali (HF, H.sub.2 O.sub.2 -NH.sub.4 OH, HCl-H.sub.2 O.sub.2 mixture) to wash away metallic polluting substances successively and finally with ultra-pure water, after which drops of the ultra-pure water are removed and the wafer is sent to the next step. The purity of the ultra-pure water used in the process is very high; the specific resistance is kept at 18 M .OMEGA..multidot.cm or above, TOC 50 ppb at or below, and the fine particles at less than 0.1 .mu.m 50 particles/ml. Nevertheless defects appear unless the drops are sufficiently removed, so that various studies have been undertaken on the method of removing water drops.
In conventional water drop removing methods, there is a drying method using hot air, a method of rotating a substrate after washing with water and mechanically dispersing water drops by centrifugal force caused by the rotation, and a method of using vapor of organic solvent such as isopropyl alcohol (IPA), replacing water by the solvent and then drying the solvent. These methods are termed a hot air drying method, a spin drying method, an IPA vapor drying method, respectively, and are used in conventional wafer washing processes.
At present, the washing of a chemical solution adhered on the wafer with ultra-pure water is effected by filling a vessel with the ultra-pure water, dipping the wafer in the ultra-pure water while overflowing the water and then replacing the chemical solution by the ultra-pure water. Further, recently, a washing method using steam which is produced by heating and evaporating the water has been reported.
In the washing of a semiconductor wafer, etc., it is desired that all of the above-described washing-drying techniques leave no impurities, for example, fine particles and soluble substances contained in solution on the surface of an object to be treated (washed object). However, the above-mentioned techniques have an unsatisfactory point, therefore, the impurities can be left on the surface. Namely, the hot air drying method evaporates water drops adhered on the surface of the substrate by hot air, so that fine particles and insoluble components in the water drops can be deposited, and finally impurities can be left on the substrate. In the spin drying method, it is impossible to remove all of the water drops, therefore, impurities can be left on the surface of the washed wafer in a similar manner to the hot air drying method when the surface, particularly, water drops in fine grooves on the surface of the wafer are dried. Further, although the IPA vapor drying method is less sensitive to the influence of impurities in the ultra-pure water since the water that is used in the washing is replaced with the IPA, it has the problem of adhesion of impurities in the IPA due to the dispersion of IPA mist and the problem of replacement between the IPA and the water. Further, in the step of washing a wafer having a chemical solution with ultra-pure water prior to a drying step, a lot of ultra-pure water is over flown, and the chemical solution of the wafer dipped in the water is replaced by the ultra-pure water, so that a lot of water is required and impurities are likely to remain on the surface as the degree of integration increases because it is not easy to achieve a sufficient washing effect in the fine grooves.
The vapor washing method also has the problem that the impurities in the vapor adhere to the surface of the object being washed and remain there.
Other prior arts concerning washing methods are disclosed Japanese Patent Laid-Open Nos. 61-174982, 61-138582, 61-138583, 61-200885, etc. for example.